System and method for holographic storage

ABSTRACT

A system and a method for holographic storage mainly involve forming a holographic interference pattern in a holographic recording medium. The holographic storage system utilizes a light source to emit a coherent beam. The coherent beam is irradiated to a first reflector to form a divergent beam. The divergent beam is then irradiated to a second reflector to form collimating beams (a signal beam and a reference beam). The signal beam goes through a spatial light modulator (SLM) and is modulated by the SLM. After that, the reference beam and the modulated signal beam are irradiated to a convergent unit, and are directed to the holographic recording medium for forming the holographic interference pattern. The holographic storage system that the light source is split into a signal beam and a reference beam by a set of reflectors according to the reflection principle without involving refraction may employ wavelength multiplexing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s).094147757 filed in Taiwan, R.O.C. onDec. 30, 2005 the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a system and method for holographicstorage, and more particularly to a system and method for holographicstorage using a set of reflectors to split a light source.

2. Related Art

At present, in the optical storage medium market, the capacity of acommercialized blue-ray disc cannot be larger than 100 GBytes, sovarious possible super capacity recording techniques are being developedin a wide range. Among these techniques, the holographic optical disc isthe one with the most potential. Though the holographic recordingtechnique has been developed for a long time, it cannot be applied toconsumer optical storage commodities- for various reasons. For example,all of the early holographic experiments required huge high-power laserlight sources of hundreds of milliwatts and complicated optical systems,and a heavy vibration-free table. Moreover, the photo-refractive crystalusually used as the holographic recording medium is more expensive thanother, more average-priced media. However, along with technical progressand conceptual changes, the limitations of the holographic storagerecording technique have been eliminated one after another. Forinstance, miniaturized high-power lasers, high photosensitive recordingmaterials, and miniature data access optical systems have beensubstantiality developed. Besides, the belief that a recording mediummust be rewritable has wavered due to consumer behavior in the opticaldisc market. Till now, it was difficult to make the recording materialof the rewritable photo-refractive crystal meet the requirements offavorable material property, high data safety, and low price. However,enlightened by the wide popularization of average-priced optical discssuch as the write-once CD-R/DVD-R, holographic recording without usingrewritable media materials has begun to be widely accepted. When notconsidering rewritability, many cheap organic materials of highphotosensibility, for example: photopolymer, can be selected as thedata-recording layer of the holographic optical disc. When thephotopolymer is irradiated by strong recording light, a chemicalreaction such as the linkage of molecules occurs. Therefore, recordingof three-dimensional holographic interference fringes of data and datareproduction can be performed via changes in optical properties causedby manipulating the density of the molecule linkage. The aforementionedconcept of miniature data access optical system having position-servofunction comes from the servo mechanism of CD/DVD optical disc drives,which is the key point in using holographic optical discs.

U.S. Patent Gazette Publications No. 20040212859 and U.S. Pat. No.6,700,686 disclose the application of the holographic storage techniquein a transmissive holographic recording medium. As it is a transmissivedesign, the image sensor is disposed at the other side of theholographic recording medium. As such, the overall volume of the systemis enlarged. Besides, the transmissive system architecture designusually has the optical axis of the object lens passing the signal beamperpendicular to the holographic recording medium, and the referencebeam must be obliquely irradiated to the holographic recording medium.Therefore, the relative position and direction between the referencebeam and the holographic recording medium deviate easily. Once thedeviation occurs, the reproduced signal beam will not be formed if thereference beam cannot be irradiated to the holographic recording mediumalong the original path. Thus, the produced signal beam cannot becaptured by adjusting the signal beam path. Therefore, the image sensorfor receiving produced light signals cannot receive any reproduced beamsignals, and, of course, it cannot recover the correct reproduced databy an image processing technique. Though for a static holographicrecording medium, the reproduced beam signal can be obtained if thearchitecture allows for scanning the position and direction of referencebeams in a small range. However, as for a continuously movingholographic recording medium, it is still hard to achieve the samepurpose of obtaining the reproduced signal.

Other relative arts disclosed in U.S. Pat. No. 6,721,076 and U.S. Pat.No. 6,909,529 provide an optical architecture for reflective holographicrecording medium. However, no specific servo methods are provided.

In addition, U.S. Pat. No. 6,909,529 provides an optical architecturefor a reflective holographic recording medium with servo. However, asthe light beams are all focused by lenses as convergent elements,wavelength multiplexing cannot be applied.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a holographic storage systemis provided. The system mainly involves forming a holographicinterference pattern in a holographic recording medium. The holographicstorage system utilizes a light source to emit a coherent beam. Thecoherent beam is irradiated to a first reflector to form a divergentbeam. The divergent beam is then irradiated to a second reflector toform collimating beams and then split the collimating beams into asignal beam and a reference beam. The signal beam goes through a SLM andis modulated by the SLM. After that, the reference beam and themodulated signal beam are irradiated to a convergent unit and thendirected to the holographic recording medium for forming the holographicinterference pattern.

According to another aspect of the invention, a holographic storagemethod is provided. In the method of the present invention, a coherentbeam is generated first and irradiated to a set of reflectors to form asignal beam and a reference beam collimating and parallel with eachother. Then, the signal beam is modulated. After that, the modulatedsignal beam and the reference beam are directed into the holographicrecording medium to generate the holographic interference pattern.

Accordingly, it is an object of the present invention to provide asystem and method for holographic storage without involving refraction;therefore, a wavelength multiplexing mechanism can be applied, and othermultiplexing mechanisms such as peristrophic multiplexing or phasemultiplexing can be added to raise the storage capacity of theholographic recording medium.

Accordingly, it is another object of the present invention to provide asystem and method for holographic storage as described above which iseasy to be fabricated due to the modularity thereof, and is compatiblewith conventional recording media such as the CD, DVD or BD (HD-DVD).

The features and practice of the preferred embodiments of the presentinvention will be illustrated in detail below with the accompanyingdrawings.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below for illustration only, and whichthus is not limitative of the present invention, and wherein:

FIG. 1 is a schematic diagram of the recording of the holographicstorage system of the invention;

FIG. 2 is a schematic diagram of the reproducing of the holographicstorage system of the invention;

FIG. 3 is a schematic diagram of the signal beam, reference beam, andservo beam directed in the holographic recording medium;

FIGS. 4A and 4B are schematic diagrams of the wavelength selector of theinvention;

FIGS. 5A and 5B are schematic comparison diagrams of the positions ofthe servo light source and the light source;

FIG. 6 is a schematic diagram of the light source diverged after beingirradiated to the first reflector and the second reflector according tothe invention;

FIGS. 7A and 7B are schematic diagrams of the convergent unit accordingto another embodiment of the invention;

FIG. 8 is a schematic diagram of the recording of the holographicstorage system according to the second embodiment of the invention;

FIG. 9 is a schematic diagram of the reproducing of the holographicstorage system according to the second embodiment of the invention;

FIGS. 10, 12, and 13 are schematic diagrams of the holographic storagesystem compatible with the traditional compact disc according to thethird embodiment of the invention.

FIG. 11 is a top view schematic diagram of the system according to thethird embodiment of the invention.

FIGS. 14, 15, and 16 are flow charts of the first method of theinvention;

FIGS. 17, 18, and 19 are flow charts of the second method of theinvention; and

FIGS. 20, 21, and 22 are flow charts of the third method of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, it is a schematic diagram of the recording of theholographic storage system according to the present invention. Thepresent invention is a holographic storage system 100 for generating aholographic interference pattern 500 in a holographic recording medium600. Therefore, the holographic storage system 100 uses a light source110 to generate a coherent beam 111. The coherent beam 111 is irradiatedto a first reflector 130 to form a divergent beam 113. The divergentbeam 113 is then irradiated to a second reflector 140 to form two beams,i.e., a signal beam 115 and a reference beam 117 as shown in FIG. 6. Aspatial light modulator (SLM) 170 is disposed in the signal beam path,to make the signal beam 115 go through the SLM 170 to become a modulatedsignal beam 115. Afterward, the reference beam 117 and the modulatedsignal beam 115 are irradiated to the convergent unit 150 to direct themodulated signal beam 115 in the holographic recording medium 600. Whenthe signal beam 115 and the reference beam 117 intersect in theholographic recording medium 600, the holographic interference pattern500 is generated and recorded in a recording layer 610 of theholographic recording medium 600. However, in order to gather theoptical efficiency of the signal beam 115 and the reference beam 117,the two beams can be modulated into two rectangular collimating beamswith the combination and adjustment of the first reflector 130 and thesecond reflector 140. Therefore, the coherent beam 111 generated by thelight source 110 can be completely converted into the signal beam 115and the reference beam 117.

Referring to FIG. 2, it is a schematic diagram of the reproducing of theholographic storage system according to the invention. When thereference beam 117 is irradiated to the holographic interference pattern500 of the holographic recording medium 600, a reproduced beam 119 isgenerated. To make the reproduced beam 119 return along the path of thereference beam 117, a wavelength selecting film 630 is added between therecording layer 610 of the holographic recording medium 600 and theservo track 650. The wavelength selecting film 630 reflects all thelights emitted by the light source, so the reproduced beam reflected bythe wavelength selecting film returns along the path of the referencebeam 117. The first beam splitter 190 is disposed on the path of thereference beam 117. When the reproduced beam 119 is irradiated to thefirst beam splitter 190, the reproduced beam 119 is reflected by thefirst beam splitter 190 to be irradiated to an image sensor 230, forreading the optical signal of the reproduced beam 119.

Moreover, in order to prevent the signal beam irradiated to theholographic recording medium 600 during the reproduction, a shutter 400is added in the path of the signal beam 115 for controlling the passingof the signal beam 115. Therefore, when the system is in a recordingstate, the shutter 400 makes the signal beam 115 go through. If thesystem is in a reproducing state, the shutter 400 blocks the signal beam115, to prevent the signal beam 115 and the reference beam 117 frombeing irradiated to the holographic recording medium 600 again andavoiding interference of the signal of the reproduced beam 119.

As the signal beam 115 goes through the SLM 170, the SLM 170 is atransmissive SLM, for example, a transmissive liquid crystal panel.

To make the holographic interference pattern 500 continuously stored inthe holographic recording medium 600, a servo track 650 is disposed inthe holographic recording medium 600. A servo beam 310 generated by aservo light source 300 is also disposed on the light source 110 forconverting the servo beam 310 into two beams in parallel afterirradiating the servo beam 310 to the first reflector 130 and the secondreflector 140. The two beams are irradiated along the paths of thesignal beam 115 and the reference beam 117 respectively, and both aredirected to the holographic recording medium 600. In order to avoidhaving the focuses of the servo beam 310 and the signal beam 115 overlapeach other, the position of the servo light source 300 is deviated fromthat of the light source 110, as shown in FIGS. 5A and 5B. As such, whenthe servo beam 310 is irradiated to the first reflector 130 andreflected to be irradiated to the second reflector 140, as the servolight source 300 and the light source 110 are located at differentpositions, the position and size of the servo beam 310 incident to thefirst reflector 130 are different. Therefore, the focuses of the servobeam 310 through the first reflector 130, the second reflector 140, andthe convergent unit 150 are different, as shown in FIG. 3. Moreover, inorder to prevent the servo beam 310 interfering in the holographicrecording medium 600, a filter 330 is added in the path of the signalbeam 115 for filtering the servo beam 310 in the path of the signal beam115. As such, only the servo beam 310 along the path of the referencebeam 117 is irradiated to the servo track 650 of the holographicrecording medium 600. The servo beam 310 is reflected after beingmodulated by the servo track 650 and is continuously transmitted towardthe path of the signal beam 115. Further, before the servo beam 310modulated by the servo track 650 goes through the filter 330, the secondbeam splitter 210 is disposed in the path of the signal beam 115 to makethe servo beam 310 modulated by the servo track 650 irradiated to thesecond beam splitter 210 and reflected to be incident to the sensingcontrol portion 350, for capturing the modulated servo beam 310. Thesignal is compatible with conventional recording media such as the CD,DVD or BD (HD-DVD). Therefore, the holographic interference pattern 500can be continuously stored in the holographic recording medium 600 alongthe servo track 650. Further, as the servo beam can go through thewavelength selecting film 630 in the holographic recording medium 600,the wavelength selecting film 630 has no negative influence. The imagesensor 230, therefore, may be a light detecting device.

Moreover, before the servo mechanism is started, the surface of theoptical axis is adjusted to be perpendicular to the recording medium.Thus, a tilt sensor 155 is added to the convergent unit 150 forfacilitating the control system (not shown) to control the oblique angleof the convergent unit 150, thereby making the signal beam 115, thereference beam 117, and the servo beam 310 perpendicularly irradiated tothe holographic recording medium 600. In the present embodiment, theoblique angle of the third reflector 151 is sensed by four tilt sensors155 respectively located at both sides of the holographic storage system100.

In order to convert the coherent beam 111 generated by the light source110 into parallel beams by irradiating the coherent beam 111 to thefirst reflector 130 and the second reflector 140, i.e., the signal beam115 and the reference beam 117. The first reflector 130 is a convexmirror, and the second reflector 140 is a concave mirror, for convertingthe coherent beam 111 into the divergent beam 113 after the coherentbeam 111 is irradiated to the first reflector 130. Then, the divergentbeam 113 is split into the signal beam 115 and the reference beam 117after being irradiated to the second reflector 140.

However, to make the signal beam 115 and the reference beam 117 as twoideal parallel beams, the first reflector 130 is a convex hyperbolicmirror and the second reflector 140 is a concave parabolic mirror. Bysuch a combination, the signal beam 115 and the reference beam 117 havebetter parallelism.

The convergent unit 150 is used to direct the signal beam 115 and thereference beam 117 in parallel again. The convergent unit 150 adopts thecombination of the third reflector 151 and a fourth reflector 153. Thethird reflector 151 converts the reference beam 117 and the modulatedsignal beam 115 into a convergent beam. After irradiated to the fourthreflector 153, the convergent beam will be directed into the holographicrecording medium 600 again and interfered with each other to generatethe holographic interference pattern 500.

Therefore, the third reflector 151 is a concave mirror and the fourthreflector 153 is a convex mirror. As such, the signal beam 115 and thereference beam 117 is directed in the holographic recording medium 600at the focus after being irradiated in parallel to the reflector 151 andthe fourth reflector 153.

Likewise, to make the signal beam 115 and the reference beam 117preferably directed into a focus, the concave mirror is a parabolicmirror, and the convex mirror is a hyperbolic mirror. Therefore, thesignal beam 115 and the reference beam 117 can be converted into twoconvergent beams after being irradiated to the third reflector 151 inthe form of a concave paraboloid. The two convergent beams are directedinto the focus by being irradiated to the fourth reflector 153 in theform of a convex hyperboloid. Thus, by disposing the holographicrecording medium 600 on the focus, the signal beam 115 and the referencebeam 117 can be directed into the holographic recording medium 600.

Referring to FIGS. 7A and 7B, they are schematic diagrams of anotherembodiment of the convergent unit according to the present invention. Inaddition to the third reflector 151 and the fourth reflector 153 whichare a concave parabolic mirror and a convex hyperbolic mirrorrespectively, the third reflector 151 and the fourth reflector 153 canbe flat mirrors but arranged according to a parabolic curve 410 and ahyperbolic curve 430. The focuses of the parabolic curve 410 and thehyperbolic curve 430 are coincident. As such, though the third reflector151 and the fourth reflector 153 are flat, they function in the same wayas a parabolic mirror and a hyperbolic mirror. As a result, the signalbeam 115 and the reference beam 117 are directed on the focus F afterbeing irradiated to the third reflector 151 arranged on the paraboliccurve 410 and the fourth reflector 153 arranged on the hyperbolic curve430.

Furthermore, the first reflector 130, the second reflector 140, thethird reflector 151, and the fourth reflector 153 can achieve therequired purpose via the combination of a spherical reflector and anaspheric reflector.

The coherent beam 111 generated by the light source 110 is split byreflecting the first reflector 130 and the second reflector 140, and theconvergent unit 150 also directs light with the third reflector 151 andthe fourth reflector 153 instead of refracting. As such, the holographicstorage system of the invention can employ a multi-wavelength lightsource 110, so there will be no color difference.

The multi-wavelength light source 110 is used to generate themulti-wavelength coherent beam 111, so the light source 110 can beformed of more than one secondary light source 121. Each secondary lightsource 121 can emit a coherent beam 111 of a certain wavelength, or thelight source 110 is tunable wavelength, such as distributed feedbacklaser (DFB Laser), vertical cavity surface emitting laser (VCSEL),wavelength-tunable carbon dioxide laser, or distributed Bragg reflectorlaser (DBR Laser).

Referring to FIGS. 4A and 4B, they are schematic diagram of thewavelength selector of the invention. The wavelength selector 123 ismainly used to select light of a certain wavelength by making thedesired light go through. As the present embodiment uses a recording andreproducing light source of a wavelength at a time, when multiplesecondary light sources 121 are used as the multi-wavelength lightsource 110, to make the recording or reproducing light source have aspecific wavelength at a time, the wavelength selector 123 can be usedto select the wavelength. Therefore, light of a certain wavelengthpasses through the selector and is irradiated to the first reflector130. The wavelength selector 123 includes an aperture stop 125 and aplate glass 127. The aperture stop 125 is used to limit the field ofview angle of the incident beam. When the plate glass 127 keeps stilland the secondary light sources 121, 121 a, and 121 b areperpendicularly irradiated to the plate glass 127, the secondary lightsources 121, 121 a, and 121 b go through the plate glass 127 directly.At this time, only the secondary light source 121 can pass through theaperture stop 125, while others are blocked. When the plate glass 127 isrotated an angle θ about the optical axis 450, the incident beam isobliquely irradiated to the plate glass 127, and the emergent beam isparallel with but a distance away from the incident beam. Therefore,when the plate glass 127 is rotated, the secondary light sources 121,121 a, and 121 b are obliquely irradiated to the plate glass 127. Then,the secondary light sources 121, 121 a, and 121 b are moved along theoptical axis 450 for a distance. As such, the secondary light source 121is blocked by the aperture stop 125, and the secondary light source 121a can pass through the aperture stop 125. As a result, light of acertain wavelength can pass through the aperture stop 125 to beirradiated to the first reflector 130 by rotating the plate glass 127.

Referring to FIGS. 8 and 9, they are schematic diagrams of the recordingand reproducing of the holographic storage system according to thesecond embodiment of the invention. The present embodiment adopts theoptical architecture of the last embodiment. However, the servo lightsource 300 is disposed at one side of the second beam splitter 210.Therefore, the servo beam 310 generated by the servo light source 300 isreflected by the second beam splitter 210 and is irradiated to theconvergent unit 150 along the path of the signal beam 115. Then, theservo beam 310 is irradiated to the servo track 650 of the holographicrecording medium 600 via the convergent unit 150. After that, the servobeam 310 is reflected to be irradiated to the convergent unit 150 againand then returns along the path of the reference beam 117. At this time,a dichroic beam splitter 370 is added in the path of the reference beam117. The dichroic beam splitter 370 can reflect light of a certainwavelength, for example, the servo beam 310 without affecting lights ofother wavelengths, so the reference beam 117 can pass through.Therefore, when the servo beam 310 returns via the convergent unit 150along the path of the reference beam 117, it is reflected by thedichroic beam splitter 370 and then irradiated to the sensing controlportion 350. The signal is compatible with conventional recording mediasuch as the CD, DVD or BD (HD-DVD). The holographic interference pattern500 can be continuously formed in the holographic recording medium 600along the servo track 650 and recorded by the holographic recordingmedium 600.

As the servo light source 300 is disposed at one side of the second beamsplitter 210 instead of at the position of the light source 110 in thelast embodiment, the servo beam 310 will not be split into two beams viathe first reflector 130 and the second reflector 140. Therefore, theservo beam 310 will not interfere with the holographic recording medium600, so the filter 330 is not necessary here.

The optical architecture of the invention can apply various multiplexingmechanisms, such as wavelength multiplexing, phase multiplexing,peristrophic multiplexing, for improving the storage capacity. If aspatial phase modulator 390 is added in the path of the reference beam117, such as ground glass, for changing phase, thereby making thepresent embodiment have a phase multiplexing mechanism. Besides, as thelight source 110 has various wavelengths, different holographicinterference patterns 500 are generated by different wavelengths.

As two beams are generated after the coherent beam 111 is irradiated tothe first reflector 130 and the second reflector 140, wherein one beampass through the SLM 170 and becomes a beam modulated by the SLM 170,i.e., the signal beam 115, and the beam symmetric to the signal beam 115about the optical axis is the reference beam 117. Therefore, when theSLM 170 is rotated about the optical axis, the incident direction of themodulated beam also rotates about the optical axis, so the holographicstorage system of the invention has a peristrophic multiplexingmechanism.

FIG. 10 is a schematic diagram of the holographic storage systemcompatible with the traditional compact disc according to the thirdembodiment of the invention. And FIG. 11 is a top view schematic diagramof the system. In FIG. 10, the whole structure is similar to that of thefirst embodiment. Therefore, the composed structure of the thirdembodiment is not discussed again. The light source 110 is used toproduce a recording/reproducing light 901. When therecording/reproducing light 901 is incident upon the first reflector130, the recording/reproducing light 901 is reflected by the firstreflector 130 and then the recording/reproducing light 901 is incidentupon the second reflector 140; two parallel recording/reproducing lights901 a, 901 b are hence formed. The recording/reproducing lights 901 a,901 b are focused on a second recording medium 910 through the thirdreflector 151 and the fourth reflector 153. Therefore, therecording/reproducing lights 901 a, 901 b may be incident upon thefocusing unit 150, and then are incident upon the second recordingmedium 910 located on the position of the holographic recording medium,so as to record data on the second recording medium 910. Again, when therecording/reproducing lights 901 a, 901 b are incident upon thedata-recorded second recording medium 910, the recording/reproducinglights 901 a, 901 b are modulated and reflected by the second recordingmedium 910. Then the lights 901 a, 901 b are incident upon the focusingunit 150 again, and then emit to the second beam splitter 210 with anincident angle form the focusing unit 150. Next, therecording/reproducing lights 901 a, 901 b emitted from the focusing unit150 turns to the incident light detecting device 990 due to thereflection by the second beam splitter 210.

In this embodiment, the light source 110 may be a blue laser, and thesecond recording medium 910 is a recording CD capable of use in the bluelaser. As shown in FIG. 11, in the third embodiment, other light sourcemay be disposed on the position of the servo light source excepting theposition of the light source such as the wavelength of 780 nm ofinfrared ray laser or the wavelength of 650 nm of red light laser. InFIG. 11, different beam splitter locations are utilized to expressdifferent optic frameworks. In this embodiment, three optic structuresare represented. One of the optic structures is depicted as shown inFIG. 10. Another two optic structures will be described later. As shownin FIGS. 12 and 13, the second light source 930 and the third lightsource 940 may represent the wavelength of 780 nm of infrared ray laserand the wavelength of 650 nm of red light laser, respectively. Thesecond light source 930 and the third light source 940 are used toproduce the recording/reproducing lights 903, 905. Therecording/reproducing lights 903, 905 are reflected and turned to thefocusing unit 150 with an incident angle. Then, the lights 903, 905 areincident upon the second recording medium 910 by the focusing unit 150,so as to record data on the second recording medium 910. If therecording/reproducing lights 903, 905 are incident upon thedata-recorded second recording medium 910, the lights 903, 905 will bemodulated by the second recording medium 910 and then will reflect themodulated recording/reproducing lights 903, 905. Then, the modulatedrecording/reproducing lights 903, 905 are incident upon the focusingunit 150 and emit to a fourth beam splitter 953 and a sixth beamsplitter 957, respectively. Again, the lights 903, 905 are incident uponthe light detecting device 990 because they are affected by the fourthbeam splitter 953 and the sixth beam splitter 957. Therefore, the secondrecording medium 910 can be the Compact Disc (CD) or Digital Video Disc(DVD) in market.

Hence, the holographic storage system not only can be used as aholographic recording but also can support the CD, DVD, and BD (HD-DVD).

Referring to FIG. 14, it is a flow chart of the first method of theinvention. A holographic storage method of the invention involves firstgenerating a servo beam incident to a servo track of a holographicrecording medium, for modulating the position of the holographicrecording medium (Step 700). After that, a coherent beam is generatedand irradiated to a set of reflectors, to make the coherent beam reflectinto a signal beam and a reference beam which are collimating and inparallel with each other (Step 710). Then, the signal beam is modulated(Step 730). The reference beam and the modulated signal beam aredirected to the holographic recording medium to form a holographicinterference pattern (Step 750).

Referring to FIG. 15, after a coherent beam is generated and irradiatedto a set of reflectors for reflecting the beam into a signal beam and areference beam that are collimating and in parallel with each other(Step 710), the position of the signal beam is changed (Step 711).Therefore, the holographic storage method has a peristrophicmultiplexing mechanism.

Referring to FIG. 16, after the signal beam is modulated (Step 730), thephase of the reference beam is changed (Step 731). Therefore, theholographic storage method has a phase multiplexing mechanism.

Or, the peristrophic multiplexing mechanism and the phase multiplexingmechanism can be added into the holographic storage method together.

Referring to FIG. 17, it is a flow chart of the second method of theinvention. A holographic storage method of the invention involves firstgenerating a coherent beam incident to a set of reflectors to form asignal beam and a reference beam that are collimating and in parallelwith each other (Step 710). Afterward, the signal beam is modulated(Step 730). The reference beam and the modulated signal beam aredirected to a holographic recording medium to form a holographicinterference pattern (Step 750). When the reference beam is irradiatedto the holographic interference pattern, a reproduced beam is generated(Step 770). The reproduced beam is then received and resolved (Step790).

Referring to FIG. 18, after a coherent beam is generated and irradiatedto a set of reflectors for reflect the beam into a signal beam and areference beam that are collimating and in parallel with each other(Step 710), the position of the signal beam is changed (Step 711).Therefore, the holographic storage method has a peristrophicmultiplexing mechanism.

Referring to FIG. 19, after the signal beam is modulated (Step 730), thephase of the reference beam is changed (Step 731). Therefore, theholographic storage method has a phase multiplexing mechanism.

Or, the peristrophic multiplexing mechanism and the phase multiplexingmechanism can be added into the holographic storage method together.

Referring to FIG. 20, it is a flow chart of the third method of theinvention. To make the holographic interference pattern continuouslyrecorded in the holographic recording medium, a method for holographicstorage and reproduction involves first generating a servo beamirradiated to a servo track of a holographic recording medium formodulating the position of the holographic recording medium (Step 700).Afterward, a coherent beam is generated and irradiated to a set ofreflectors for being reflected into a signal beam and a reference beamthat are collimating and in parallel with each other (Step 710). Then,the signal beam is modulated (Step 730). The reference beam and themodulated signal beam are directed to the holographic recording mediumto generate a holographic interference pattern (Step 750).

When the reference beam is irradiated to the holographic interferencepattern, a reproduced beam is generated (Step 770). The reproduced beamis then received and resolved (Step 790).

Referring to FIG. 21, after a coherent beam is generated and irradiatedto a set of reflectors for reflecting the beam into a signal beam and areference beam that are collimating and in parallel with each other(Step 710), the position of the signal beam is changed (Step 711).Therefore, the method for holographic storage and reproduction has aperistrophic multiplexing mechanism.

Referring to FIG. 22, after the signal beam is modulated (Step 730), thephase of the reference beam is changed (Step 731). Therefore, the methodfor holographic storage and reproduction has a phase multiplexingmechanism.

Or, the peristrophic multiplexing mechanism and the phase multiplexingmechanism can be added into the method for holographic storage andreproduction together.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims

1-14. (canceled)
 15. A holographic storage system, for generating aholographic interference pattern in a holographic recording medium, theholographic storage system comprising: a light source, for generating acoherent beam; a first reflector, for reflecting the coherent beam toform a divergent beam; a second reflector, for reflecting the divergentbeam and splitting it into a signal beam and a reference beam; a SLM,for modulating the signal beam; a convergent unit, for directing thereference beam and the modulated signal beam to the holographicrecording medium to form the holographic interference pattern; a firstbeam splitter, disposed in the path of the reference beam, forgenerating a reproduced beam when the reference beam is irradiated tothe holographic interference pattern, wherein the reproduced beamreturns along the path of the reference beam, and is irradiated to thefirst beam splitter and reflected to be irradiated to an image sensor; asecond beam splitter, disposed in the path of the signal beam; and aservo light source, for generating a servo beam, wherein the servo beamis irradiated to the first reflector, the second reflector, and theconvergent unit, and directed to a servo track of the holographicrecording medium; then, the servo beam is reflected by the servo trackand irradiated to the convergent unit again; afterward, the servo beamreturns along the original path of the signal beam and is irradiated tothe second beam splitter; then is reflected and then incident to asensing control portion, to make the holographic interference patterncontinuously recorded in the holographic recording medium along theservo track.
 16. The holographic storage system according to claim 15,wherein the first reflector is a convex mirror, and the second reflectoris a concave mirror, for splitting the coherent beam sequentiallyirradiated to the convex mirror and the concave mirror into the signalbeam and the reference beam in parallel.
 17. The holographic storagesystem according to claim 15, wherein the SLM is a transmissive SLM. 18.The holographic storage system according to claim 15, wherein the lightsource is a multi-wavelength light source, for generating the coherentbeam of multiple wavelengths.
 19. The holographic storage systemaccording to claim 18, wherein the multi-wavelength light source isformed of more than one secondary light source emitting the coherentbeams of a certain wavelength.
 20. The holographic storage systemaccording to claim 19, further comprising a wavelength selector, whereinthe wavelength selector includes: an aperture stop, for limiting thefield of view angle of the incident beam; and a plate glass, to make theincident beam be parallel with the emergent beam but deviated from it bya certain distance when rotating, and thus making the incident beamirradiated to the aperture stop, thereby limiting a wavelength pass forthe secondary light source, so as to let the coherent beam with thecertain wavelength irradiate to the first reflector.
 21. The holographicstorage system according to claim 18, wherein the multi-wavelength lightsource is a wavelength-tunable light source.
 22. The holographic storagesystem according to claim 15, wherein the convergent unit comprises: athird reflector, for converting the reference beam and the modulatedsignal beam into a convergent beam; and a fourth reflector, fordirecting the convergent beam into the holographic recording medium, andcausing an interference with each other to form the holographicinterference pattern.
 23. The holographic storage system according toclaim 22, wherein the third reflector is a concave mirror, and thefourth reflector is a convex mirror, to make the signal beam and thereference beam incident in parallel to the third reflector and thefourth reflector being directed in the holographic recording medium atthe focus.
 24. (canceled)
 25. The holographic storage system accordingto claim 15, further comprising a filter for filtering the servo beam,wherein the filter is disposed in the path of the signal beam forfiltering the servo beam in the path of the signal beam.
 26. Theholographic storage system according to claim 15, further comprising anSLM disposed in the path of the reference beam for changing the phase ofthe reference beam.
 27. The holographic storage system according toclaim 15, further comprising a shutter for controlling the passing ofthe light, wherein the shutter is disposed in the path of the signalbeam for controlling the passing of the signal beam. 28-44. (canceled)